Tuesday, 18 October 2016


1) A passive attack is a network attack in which a system is monitored and sometimes scanned for open ports and vulnerabilities. The purpose is solely to gain information about the target and no data is changed on the target.Passive attacks have to do with eavesdropping on, or monitoring, transmissions. Electronic mail, file transfers, and client/server exchanges are examples of transmissions that can be monitored. Passive threat are very difficult to detect and equally difficult to prevent as well, where as active threats continue to make a changes to the system, they are easy to find out & fix as well.Malicious misuse/malicious intent is any from of tampering of the computer system which includes penetration or any form of illegal attraction of the computer which also includes the generation of illegal codes to alter the standard codes within the system.

An active attack is a network exploit in which a hacker attempts to make changes to data on the target or data en route to the target. Types of active attacks: In a masquerade attack, the intruder pretends to be a particular user of a system to gain access or to gain greater privileges than they are authorized for.Sabotage ,Accident Errors and Espionage Agents are all active threats.

2)  Varray stands for variable-size array. Varray can be stored in the columns of your tables. When you create varrays you must provide the maximum size for them. They retain their ordering and subscripts when stored in and retrieved from a database table. They are similar to PL/SQL table, and each element in a varray is assigned a subscript/index starting with 1.These are dense and Not sparse, which means there is no way to delete individual elements of a Varray.

3)The data dictionary is full of 'Metadata', information about what is going-on inside your database.The data dictionary is created when the Oracle database is created. It is owned by the SYS user, and is stored principally in the SYSTEM tablespace, though some components are stored in the SYSAUX tablespace in Oracle Database 10g. The data dictionary is comprised of a number of tables and Oracle views.No Oracle user should ever alter (UPDATEDELETE, or INSERT) any rows or schema objects contained in the SYS schema, because such activity can compromise data integrity. The security administrator must keep strict control of this central account.

4)Spanning Tree Protocol (STP) is a Layer 2 protocol that runs on bridges and switches. The specification for STP is IEEE 802.1D. The main purpose of STP is to ensure that you do not create loops when you have redundant paths in your network. Loops are deadly to a network.

5)Every Oracle Database must have a method of maintaining information that is used to roll back, or undo, changes to the database. Such information consists of records of the actions of transactions, primarily before they are committed. These records are collectively referred to as undo.
Undo records are used to:
  • Roll back transactions when a ROLLBACK statement is issued
  • Recover the database
  • Provide read consistency
  • Analyze data as of an earlier point in time by using Oracle Flashback Query
  • Recover from logical corruptions using Oracle Flashback features.

Oracle provides a fully automated mechanism, referred to as automatic undo management, for managing undo information and space. In this management mode, you create an undo tablespace, and the server automatically manages undo segments and space among the various active sessions.You set the UNDO_MANAGEMENT initialization parameter to AUTO to enable automatic undo management. A default undo tablespace is then created at database creation. An undo tablespace can also be created explicitly. The methods of creating an undo tablespace are explained in "Creating an Undo Tablespace".When the instance starts, the database automatically selects the first available undo tablespace. If no undo tablespace is available, then the instance starts without an undo tablespace and stores undo records in the SYSTEM tablespace. This is not recommended in normal circumstances, and an alert message is written to the alert log file to warn that the system is running without an undo tablespace.
6) The BIOS (Basic Input/Output System and also known as the System BIOSROM BIOS or PC BIOS) is a type of firmware used to perform hardware initialization during the booting process (power-on startup) on IBM PC compatible computers, and to provide run time services for operating systems and programs.The BIOS firmware is built into personal computers (PCs), and it is the first software they run when powered on. 

7) RSA is one of the first practical public-key cryptosystems and is widely used for secure data transmission. In such a cryptosystem, the encryption key is public and differs from the decryption key which is kept secret. In RSA, this asymmetry is based on the practical difficulty of factoring the product of two large prime numbers, thefactoring problem. RSA is made of the initial letters of the surnames of Ron RivestAdi Shamir, and Leonard Adleman, who first publicly described the algorithm in 1977. RSA is a relatively slow algorithm, and because of this it is less commonly used to directly encrypt user data. More often, RSA passes encrypted shared keys for symmetric key cryptography which in turn can perform bulk encryption-decryption operations at much higher speed.

8) INITRANS is a block level storage parameter which can be specified while creating a object (table). INITRANS and MAXTRANS parameters are used to control the concurrent access to the same block. There can be a maximum of 255 concurrent sessions that can access a block at any given time. So the maximum value for MAXTRANS parameter is 255. The value specified through INITRANS are taken into consideration for creating the initial number of ITLs (Intersted Transaction Entries) in the block.While creating the table if INITRANS 20 is specified, then 20 different ITL slots will be created in the block transaction variable header.
Each and every ITL entry in the block transaction variable header takes 24 bytes. Though a block can have a maximum of 255 different ITLs , the block is quite limited to allocate only some defined ITLs in the header. The database block size plays a important role in allocating the number of inital ITLs for the blocks.

9)Data mining (sometimes called data or knowledge discovery) is the process of analyzing data from different perspectives and summarizing it into useful information - information that can be used to increase revenue, cuts costs, or both. Data mining software is one of a number of analytical tools for analyzing data. It allows users to analyze data from many different dimensions or angles, categorize it, and summarize the relationships identified. Technically, data mining is the process of finding correlations or patterns among dozens of fields in large relational databases.Case based reasoning(CBR) is the process of solving new problems based on the solutions of similar past(real world) problems.Example: an auto mechanic who fixes an engine by recalling another car that exhibited similar symptoms is using a case based reasoning.
10)If there are n people communicating using a symmetric crptosystem, and each pair of people share a keys pair then there will be a total of [n+(n-1)]/2 pair of keys required. So for 20 people, 190 keys needed.
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